It is well known that polyolefins such as crystalline polypropylene are prepared using "Ziegler-Natta catalysts" comprising compounds of Group IV to Group VI transition metals of the periodic table and organometallic compounds of Group I to Group III metals of the periodic table. Further, processes to obtain crystalline polyolefins of high stereoregularity with high polymerization activity using these catalysts have been earnestly studied.
For example, Japanese Patent Laid-Open Publications No. 209207/1986, No. 104810/1987, No. 104811/1097, No. 104812/1987, No. 104813/1987, No. 311106/1989, No. 318011/1989 and No. 166104/1990 describe that when an olefin is polymerized using a catalyst formed from a titanium-containing solid catalyst component which comprises titanium, magnesium, halogen and an electron donor, an organoaluminum compound and an electron donor, high polymerization activity is obtained and polyolefin of high stereoregularity can be obtained.
Also the present applicant has made various researches on the olefin polymerization catalysts and processes for olefin polymerization by which crystalline polyolefins of high stereoregularity can be obtained with high polymerization activity, and has made a great number of proposals (e.g., Japanese Patent Laid-Open Publications No. 108385/1975, No. 126590/1975, No. 20297/1976, No. 28189/1976, No. 64586/1976, No. 92885/1976, No. 136625/1976, No. 87489/1977, No. 100596/1977, No. 147688/1977, No. 104593/1977, No. 2580/1978, No. 40093/1978, No. 40094/1978, No. 43094/1978, No. 135102/1980, No. 135103/1980, No. 152710/1980, No. 811/1981, No. 11908/1981, No. 18606/1981, No. 83006/1983, No. 138705/1983, No. 138706/1983, No. 138707/183, No. 138708/1983, No. 138709/1983, No. 138710/1983, No. 138715/1983, No. 138720/1983, No. 138721/1983, No. 215408/1983, No. 47210/1984, No. 117508/1984, No. 117509/1984, No. 207904/1984, No. 206410/1984, No. 206408/1984, No. 206407/1984, No. 69815/1986, No. 69821/1986, No. 69822/1986, No. 69823/1986, No. 22806/1988, 95208/1988, No. 199702/1988, No. 199703/1988, No. 202603/1988, No. 202604/1988, No. 223008/1988, No. 223009/1988, No. 264609/1988, No. 87610/1989, No. 156305/1989, No. 77407/1990, No. 84404/1990, No. 229807/1990, No. 229806/1990 and No. 229805/1990).
In the production of polyolefins, the productivity can be more enhanced and the production cost can be more reduced by the use of olefin polymerization catalysts having higher activity. Further, also from the viewpoints of "environmental problem" such as harmfulness of catalysts and "environmental protection" such as recycling of resources, the amounts of catalysts contained in the polyolefins are desired to be as small as possible, and consequently it becomes more and more important to increase catalytic activity and to prepare polyolefins in high yields per catalyst unit.
As described above, the olefin polymerization catalyst and the olefin polymerization process, by the use of which an olefin can be polymerized with much higher activity and polyolefin of high stereoregularity can be prepared, are of industrially great value, and the advent thereof is eagerly desired.